Functionalized carbon nanotubes

ABSTRACT

A material comprises a carbon nanotube and a methyl methacrylate group covalently bonded to a surface of the carbon nanotube. In some examples, the material can further comprise a polymeric chain appended to the surface of the carbon nanotube via the methyl methacrylate group. In some examples, the polymeric chain can include styrene monomer repeating units and butadiene monomer repeating units. In some examples, the polymeric chain can include a flame retardant moiety appended thereon and/or flame retardant monomer repeating units. In some examples, the carbon nanotube can be incorporated or combined with a resin material to provide a composite component. A method to produce a carbon nanotube having a polymeric chain appended thereto is also described.

BACKGROUND

The present disclosure relates to functionalized carbon nanotubes. Thesefunctionalized carbon nanotubes have potential uses as fillers inpolymeric materials, and more specifically, have applications as impactmodifiers and/or flame retardants in polymeric materials.

Carbon nanotubes (CNTs) have been previously explored as fillermaterials to impart properties to polymeric materials and resins.Nanocomposite materials incorporating CNTs are known in which the CNTsare simply mixed or blended with a matrix resin material, similar inconcept to existing carbon fiber composites. A variety of functionalizedor modified CNTs have been developed. These functionalized CNTs have, insome instances, been covalently bonded to polymeric matrix resins, butcan have separate applications as well. Of particular concern is the useof filler materials to impart improved performance to compositematerials with respect to ignition resistance, flame resistance, and/orimpact resistance.

SUMMARY

According to one embodiment of the present disclosure, a materialcomprises a carbon nanotube and a methyl methacrylate group covalentlybonded to a surface of the carbon nanotube. In some examples, thematerial can further comprise a polymeric chain appended to the surfaceof the carbon nanotube via the methyl methacrylate group. In someexamples, the polymeric chain can include styrene monomer repeatingunits and butadiene monomer repeating units. In some examples, thepolymeric chain can include a flame retardant moiety appended thereonand/or flame retardant monomer repeating units.

According to another embodiment, a composite component includes a resinmaterial and a carbon nanotube embedded or encased in the resinmaterial. The carbon nanotube has a methyl methacrylate group covalentlybonded to a surface of the carbon nanotube, and a polymeric chain isappended to the surface of the carbon nanotube via the methylmethacrylate group. In some examples, the polymeric chain can includestyrene monomer repeating units and butadiene monomer repeating units.In some examples, the polymeric chain can include a flame retardantmoiety appended thereon and/or flame retardant monomer repeating units.

According to still another embodiment, a method comprises bonding acarbon nanotube having a carboxylic acid functional group on a surfacethereof with an acyl halide to provide a methacrylic functional group onthe surface of the carbon nanotube, and copolymerizing the methacrylicfunctional group with at least one other monomer unit including avinylic functional group to provide a polymeric chain appended to thesurface of the carbon nanotube via the methacrylic function group.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 depicts a reaction of a carboxylic acid functionalized carbonnanotube with an acyl halide to provide a carbon nanotube with apolymerizable functional group.

FIG. 2 depicts a co-polymerization of co-monomers with the carbonnanotube having a polymerizable functional group to provide a carbonnanotube having polymeric groups attached thereon.

FIG. 3 is an example reaction scheme for the preparation of a carbonnanotube (CNT) having methyl methacrylate functional groups orthogonallydisposed thereon.

FIG. 4 depicts a copolymerization process providing CNTs orthogonallyfunctionalized with poly(methyl methacrylate-co-styrene-co-butadiene).

FIG. 5 depicts a copolymerization process providing CNTs orthogonallyfunctionalized with poly(methylmethacrylate-co-styrene-co-butadiene-co-(2-(diphenlyphoshate)ethylmethacrylate).

FIG. 6 depicts a copolymerization process providing CNTs orthogonallyfunctionalized with poly(methyl methacrylate-co-styrene-co-butadiene)and diphenylphosphino styrene groups.

DETAILED DESCRIPTION

The present disclosure relates to polymeric materials and fillermaterials which can be incorporated into polymeric materials to improvevarious characteristics of the polymeric material. For example, acomposite material with improved flame retardance, as compared to thepolymeric material alone, can be formulated by incorporating a fillerhaving flame retardant properties. Similarly, a composite material withimproved mechanical properties (e.g., impact resistance), as compared tothe polymeric material alone, can be formulated by incorporating afiller that imparts greater rigidity, or some other desirable physicalproperty. However, in some instances, high filler loading levels canadversely affect the properties of the composite material. For example,flame retardant fillers might alter the mechanical properties of thecomposite. Likewise, a filler incorporated to improve mechanicalproperties may cause the composite to be more combustible. The presentdisclosure concerns materials that can be used as filler materials forimproving properties of a polymeric material. In some examples, onlyimprovements in mechanical properties of the final composite materialare specifically addressed by inclusion of the filler material. In otherexamples, improvements in both flame resistance and mechanicalproperties are provided by inclusion of the filler material.

In a particular example, the filler comprises a carbon nanotube (CNT)having orthogonal functionality that can be used to improve impactresistance of polymeric material incorporating the filler. In a moreparticular example, the CNT may be functionalized with a methylmethacrylate group. The functionalized CNT incorporating such a groupmay be copolymerized with other constituent monomers to form acomposite-type material having improved impact resistance. In aparticular example, the functionalized CNT may be incorporated into astyrene-butadiene polymeric material in which the CNT is covalentlybonded to the surrounding polymeric material. In some examples, improvedflame retardation properties may be provided to the composite materialby inclusion of various co-monomers having flame retardant properties,such as acrylic, styrenic, or vinylic monomers having flame-quenchingmoieties (e.g., phosphorous, halogens, etc.) thereon. In someimplementations, the functionalized CNT can be copolymerized withstyrene, butadiene, and a flame retardant monomer to provide acomposite-type material having improved impact resistance and flameretardant properties as compared to a poly(butadiene-co-styrene) inwhich CNTs and flame retardant fillers are simply physically blended.Carbon nanotubes are known to be high strength, in terms of tensilestrength and elastic modulus, and can be electrically conductive. Assuch, composite-type materials incorporating CNTs have a variety of usesincluding in flexible solar cells, any existing composite materialapplication requiring high mechanical strength, and/or flame retardationproperties, and/or applications requiring dissipation of electrostaticenergy in some manner. The composite-type materials incorporating CNTsin this manner can be further blended or compounded with other polymers.

FIG. 3 illustrates an example reaction scheme for the preparation of aCNT having methyl methacrylate functional groups orthogonally disposedthereon.

The carboxylic acid (—COOH) functional groups on the starting materialCNT in FIG. 3 can be prepared by various means, such as an “acidcutting” method or a “nucleophilic addition” method (which requiresquenching with carbon dioxide). The carboxylic acid functionalized CNTstarting material is reacted with methacroyl chloride via a nucleophilicacyl substitution to give a methacrylic anhydride group on the surfaceof the CNT. These methacrylic groups are subsequently available forpolymerization (or copolymerization).

Radical polymerization techniques, such as use of thermal initiators,photoinitiators, and controlled (living) free radical polymerization,can be adopted for use with the methacrylic-functionalized CNTs. Forexample, various vinylic, styrenic, and/or conjugated diene co-monomerscan be polymerized along with the functionalized CNT. For example, asdepicted in the following reaction scheme (FIG. 4), styrene andbutadiene monomers can be copolymerized with the functionalized CNTproduct from FIG. 3.

FIG. 4 depicts a copolymerization process providing CNTs orthogonallyfunctionalized with poly(methyl methacrylate-co-styrene-co-butadiene).The initiator can be a free radical producing compound triggered byheat, light, or other stimuli. Here, the product CNT is covalentlylinked (via the methyl methacrylate group) to apoly(styrene-co-butadiene) (PBS) chain. Properties of the PBS can betuned according to relative ratios of styrene to butadiene, and/orcontrol of polymerization conditions and resulting chain morphology. Forexample, a block copolymer of PBS can have significantly differentproperties from a random copolymer of PBS.

Additional monomer types can be copolymerized with themethacrylic-functionalized CNT from FIG. 3. In a particular example(FIG. 5), a flame retardant (FR) moiety can be incorporated in theproduct CNT. Here, the FR moiety is depicted as a diphenylphosphate-functionalized methacrylate monomer, but other monomers havinga FR moiety may be adopted, such as a phosphate-functionalized styrenemonomer, halogenated acrylate monomers, brominated styrene monomer, andother phosphate-functionalized acrylate monomers.

FIG. 5 depicts a copolymerization process providing CNTs orthogonallyfunctionalized with poly(methylmethacrylate-co-styrene-co-butadiene-co-(2-(diphenlyphoshate)ethylmethacrylate). The initiator can be a free radical producing compoundtriggered by heat, light, or other stimuli. Here, the product CNT iscovalently linked (via the methyl methacrylate group) to apoly(styrene-co-butadiene) (PBS) chain including additional methacrylategroups having an FR moiety. Properties of the PBS chain can be variedaccording to relative ratios of styrene to butadiene and/or control ofpolymerization conditions and resulting chain morphology. The number ofFR moieties incorporated can likewise be controlled by changes in feedratio and/or polymerization conditions. It should be noted that the PBSchain depicted in the FIG. 5 product has an FR moiety appended at aposition farthest from the CNT surface, such is not a requirement andthe FR moieties can be dispersed throughout the PBS chain at variouspoints. The notation used to depict the product compound of FIG. 5 isnot intended to imply any particular PBS chain morphology and the PBSchain can be random, block, alternating, or combinations of theseaccording to the selection of polymerization conditions and techniques.

FIG. 6 depicts the synthesis of a CNT impact modifier/fillerfunctionalized with poly(methyl methacrylate-co-styrene-co-butadiene)and phosphine-functionalized styrene. Here, the product CNT from FIG. 3is copolymerized with styrene, butadiene, 4-(diphenylphosphino)styrene,and diphenyl(4-styrenyl)phosphine oxide by a radical polymerizationtechnique.

FIG. 6 depicts a copolymerization process providing CNTs orthogonallyfunctionalized with poly(methyl methacrylate-co-styrene-co-butadiene)and diphenylphosphino styrene groups. The diphenylphosphino group hasflame retardant (FR) characteristics. The initiator can be a freeradical producing compound triggered by heat, light, or other stimuli.Thus again, as was the case with FIG. 5, the product CNT of FIG. 6 iscovalently linked (via the methyl methacrylate group) to apoly(styrene-co-butadiene) (PBS) chain including a FR moiety—in thisinstance, a diphenylphosphino group. The FR moiety can also be adiphenyl(4-styrenyl)phosphine oxide derived group. In general,properties of the PBS chain can be varied according to relative ratiosof styrene to butadiene, and/or control of polymerization conditions andresulting chain morphology. The number of FR moieties incorporated canlikewise be controlled by changes in feed ratio and/or polymerizationconditions. It should be noted that the PBS chain depicted in the FIG. 6product has an FR moiety appended at a position farthest from the CNTsurface, such is not a requirement and the FR moieties can be dispersedthroughout the PBS chain at various points. The notation used to depictthe product compound of FIG. 6 is not intended to imply any particularPBS chain morphology and the PBS chain can be random, block,alternating, or combinations of these according to the selection ofpolymerization conditions and techniques.

FIG. 1 depicts a chemical reaction in which a carboxylic acidfunctionalized CNT 100 is reacted with a reactant 110 to form apolymerizable CNT 120 in which the polymerizable moiety is an orthogonalfunctional group. In this context, an orthogonal functional group is agroup attached to the outer side surface of the carbon nanotube.Reactant 110 is an acyl halide (RCOX, where X is halide and R includescarbons). In the particular example reaction depicted in FIG. 1, theacyl halide is methacryloyl chloride (also referred to as2-methylprop-2-enoyl chloride) and the polymerizable CNT 120 thusincorporates a methyl methacrylate moiety. However, the chemicalreaction is not limited to these specific example compounds and in otherinstances the reactant 110 may other acyl halides such as acroyloylchloride, ethacryloyl chloride, propacryloyl chloride, etc. In someinstances, the reaction may be conducted in the presence of catalysts,solvents, proton scavengers, or the like. In some instances, it may bepreferred to first protect the vinyl moiety of the acyl halide toprevent or limit unwanted side reactions. The ratio of reactant 110 toCNT 100 (or more particularly, the carboxylic acid functional groups ofCNT 100) can be varied. Reactant 110 may be provided to the reactionmixture in a stoichiometric ratio, in a sub-stoichiometric amount, or inexcess.

FIG. 2 depicts a chemical reaction of polymerizable CNT 120 with avariety of co-monomers. In particular, CNT 120 is copolymerized withco-monomer 210, co-monomer 220, and co-monomer 230 to form a modifiedCNT 250. Inclusion of co-monomer 230 is optional. Co-monomer 210 is, forexample, a styrene monomer or another compound incorporating a styrenicfunctional group. In the particular example depicted in FIG. 2,co-monomer 210 is styrene. Co-monomer 220 is, for example, a1,3-butadiene monomer or another compound incorporating a 1,3 dienylmoiety available for polymerization reactions. In the particular exampledepicted in FIG. 2, co-monomer 220 is a 1,3-butadiene. Co-monomer 230is, for example, a monomer incorporating a flame retardant moiety orotherwise having flame retardant characteristics. In some examples,co-monomer 230 can be a 4-diphenylphosphino styrene, adiphenyl(styrenyl)phosphine oxide, an acrylic monomer with aphosphorous-based flame retardant moiety, a brominated styrene, abrominated vinylbiphenyl, a brominated vinylnapthalene, a brominatedvinyl-diphenylethane, a brominated vinylalkane (cyclic or acyclic,C₆-C₁₂), or an acrylic monomer with a halogen-based flame retardantmoiety. In the particular example depicted in FIG. 2, co-monomer 230 is4-bromostyrene. Brominated styrenes, brominated vinylbiphenyls,brominated vinylnapthalenes, brominated vinyl-diphenylethanes, andbrominated vinylalkanes (cyclic or acyclic, C₆-C₁₂) may be referred toas “brominated monomer units.” The polymerization process includesinitiator 240, which in this instance is a free radical generator. Therelative ratio of co-monomers and CNT 120 can result in modified CNT 250having different properties or characteristics. For example, arelatively large amount of co-monomer 230 may increase the flameresistance when a greater number of flame resistance moieties areincorporated into the resulting modified CNT 250. Likewise, reactionconditions and polymerization methods can alter the properties of themodified CNT. For example, appending relatively long chains to CNT 120might increase the compatibility of the resulting modified CNT 250 incertain blends; however, long chains might limit the number orobtainable loading of CNTs in the blended material, which mightadversely reduce strength of the blended material. In general, longerpolymer chain lengths can be obtained by longer reaction times and lowerinitiator loadings. In general, shorter polymer chain lengths can beobtained by shorter reaction times and higher initiator loadings. Asdiscussed above with FIGS. 4, 5, and 6, reaction conditions andpolymerization techniques can be adopted to alter the morphology as wellas the composition of the polymer chains appended to the final productCNT. For example, sequencing of the introduction (and/or removal) ofvarious co-monomers to the reaction mixture during the polymerizationprocess can result in block type polymer chains. Similarly, control offeed stock ratios and reaction times can alter reaction productmorphology.

The modified CNT 250 may be included in or otherwise form a portion of acarbon composite material. The modified CNT 250 may be compounded with,blended with, mixed with, or otherwise combined with other polymericmaterials. For example, modified CNT 250 can be blended with a polylaticacid, a polycarpolactone, a polyamide, a polyglycolic acid, apolyhydroxybutyrate, a polyhydroxyalkanoate, a polyethyleneterephthalate, a polypropylene, a polyethylene, a plaststarch material,a polycarbonate, or a combination of the preceding, or a copolymer ofthe preceding.

The modified CNT 250 may be blended with another polymer or otherpolymers as an additive to improve impact resistance of the resultingblend, to improve resistance of the resulting blend to flames orignition, to modify rheological properties of the resulting blend, orcombinations of the preceding reasons.

In some embodiments, the modified CNT 250 may have more than one type ofpolymeric chain attached thereto. In some examples, the polymeric chainsattached to the carbon nanotube(s) may be or include polyurethane,nylon, or polyethene or derivatives of these materials. In general,particular characteristics of the appended polymer chains may differ inaspects such as chain length and ratio of monomeric repeating groups,and the like. That is, the attached polymer chains are not required toeach have the same chain length or ratio(s) of monomeric repeat groups.It is also not required that every possible carboxylic acid group on thecarbon nanotube be functionalized in the same manner. Some may be leftunreacted or may be functionalized in a different manner by, forexample, a competing reactive process or by purposeful differentiationof reactive sites in some manner, such as protection of a subset of thecarboxylic acid groups sites prior to the reaction with the acyl halide.In some embodiments, a crosslinker (e.g., a trivalent monomer unit) maybe incorporated into the reaction mixture to provide cross-linkedpolymeric connections between CNTs.

The carbon nanotubes in the figures and examples are depicted assingle-walled carbon nanotubes (SWNTs); however, the present disclosurecan also be applied to multi-walled carbon nanotubes (MWNTs). Ingeneral, functionalizations of MWNTs would occur on outer peripheralwalls. Other fullerenes besides nanotubes could be similarly modifiedaccording to the methods disclosed in the nanotube examples. Forexample, spherical or ellipsoid fullerenes could be adopted in place ofor in addition to nanotubes. Furthermore, graphene materials couldsimilarly be modified according to the disclosed methods.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

In the following, reference is made to embodiments presented in thisdisclosure. However, the scope of the present disclosure is not limitedto specific described embodiments. Instead, any combination of thefollowing features and elements, whether related to differentembodiments or not, is contemplated to implement and practicecontemplated embodiments. Furthermore, although embodiments disclosedherein may achieve advantages over other possible solutions or over theprior art, whether or not a particular advantage is achieved by a givenembodiment is not limiting of the scope of the present disclosure. Thus,the described aspects, features, embodiments and advantages are merelyillustrative and are not considered elements or limitations of theappended claims except where explicitly recited in a claim(s). Likewise,reference to “the invention” shall not be construed as a generalizationof any inventive subject matter disclosed herein and shall not beconsidered to be an element or limitation of the appended claims exceptwhere explicitly recited in a claim(s).

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

What is claimed is:
 1. A material, comprising: a carbon nanotube; amethacrylate group covalently bonded to a surface of the carbonnanotube; and a polymeric chain appended to the surface of the carbonnanotube via the methacrylate group, wherein the polymeric chainincludes a styrene monomer unit, a butadiene monomer unit, and a halogenmoiety.
 2. The material of claim 1, wherein the halogen moiety is ahalogenated acrylate monomer unit.
 3. The material of claim 1, whereinthe halogenated moiety is a brominated functionalized monomer unit. 4.The material of claim 1, wherein the styrene monomer unit is aphosphorous-containing styrenic monomer unit.
 5. The material of claim4, wherein the phosphorous-containing styrenic monomer unit is a4-(diphenylphosphino)styrene monomer unit, adiphenyl(4-styrenyl)phosphine oxide monomer unit, or a combinationthereof.
 6. The material of claim 1, further comprising: a secondmethacrylate group covalently bonded to the surface of the carbonnanotube; and a second polymeric chain appended to the surface of thecarbon nanotube via the second methacrylate group, wherein the secondpolymeric chain includes at least one of a styrene monomer unit, abutadiene monomer unit, or a phosphate-functionalized acrylate monomerunit.
 7. The material of claim 6, wherein the second polymeric chainincludes at least one of a 4-(diphenylphosphino)styrene monomer unit ora diphenyl(4-styrenyl)phosphine oxide monomer unit.
 8. A material,comprising: a carbon nanotube; a methacrylate group covalently bonded toa surface of the carbon nanotube; and a polymeric chain appended to thesurface of the carbon nanotube via the methacrylate group, wherein thepolymeric chain includes at least one of a brominated monomer unit and aphosphorous-containing styrenic monomer unit.
 9. The material of claim8, wherein the polymeric chain includes a butadiene monomer unit. 10.The material of claim 8, wherein the brominated monomer unit is at leastone of a brominated styrene monomer unit, a brominated vinylbiphenylmonomer unit, a brominated vinylnapthalene monomer unit, a brominatedvinyl-diphenylethane monomer unit, an acyclic brominated vinylalkanemonomer unit, a cyclic brominated vinylalkane monomer unit, or anacrylic monomer unit with a halogen-based flame retardant moiety,wherein the halogen-based flame-retardant moiety includes a bromine. 11.The material of claim 8, wherein the brominated monomer unit is4-bromostyrene.
 12. The material of claim 8, wherein thephosphorous-containing styrenic monomer unit includes at least one of4-(diphenylphosphino)styrene monomer unit or adiphenyl(4-styrenyl)phosphine oxide monomer unit.
 13. The material ofclaim 8, further comprising: a second methacrylate group covalentlybonded to the surface of the carbon nanotube; and a second polymericchain appended to the surface of the carbon nanotube via the secondmethacrylate group, wherein the second polymeric chain includes at leastone of a styrene monomer unit, a butadiene monomer unit, or aphosphate-functionalized acrylate monomer unit.
 14. The material ofclaim 13, wherein the second polymeric chain includes at least one of a4-(diphenylphosphino)styrene monomer unit or adiphenyl(4-styrenyl)phosphine oxide monomer unit.
 15. A material,comprising: a carbon nanotube; a methacrylate group covalently bonded toa surface of the carbon nanotube; and a polymeric chain appended to thesurface of the carbon nanotube via the methacrylate group, wherein thepolymeric chain includes at least one of a 4-(diphenylphosphino)styrenemonomer unit or a diphenyl(4-styrenyl)phosphine oxide monomer unit. 16.The material of claim 15, wherein the polymeric chain includes abrominated monomer unit selected from the group consisting of abrominated styrene monomer unit, a brominated vinylbiphenyl monomerunit, a brominated vinylnapthalene monomer unit, a brominatedvinyl-diphenylethane monomer unit, an acyclic brominated vinylalkanemonomer unit, a cyclic brominated vinylalkane monomer unit, and anacrylic monomer unit with a halogen-based flame retardant moiety,wherein the halogen-based flame-retardant moiety includes a bromine. 17.The material of claim 16, wherein the polymeric chain includes abutadiene monomer unit.
 18. The material of claim 16, furthercomprising: a second methacrylate group covalently bonded to the surfaceof the carbon nanotube; and a second polymeric chain appended to thesurface of the carbon nanotube via the second methacrylate group,wherein the second polymeric chain includes at least one of a styrenemonomer unit, a butadiene monomer unit, or a phosphate-functionalizedacrylate monomer unit.